The invention relates in general to radio-frequency antennas and in particular to antenna constructions that include several radiating elements which can be taken into use through actions by the user. In addition, the invention is directed to decreasing that portion of the energy radiated by the antenna which is absorbed by the user of the radio apparatus.
Many kinds of requirements are set on the antennas of portable radio apparatuses. The antenna construction should be small and compact. Advantageously, it should include a movable part which, when pulled out, enhances the operation of the antenna compared to the position where the movable part is in the transport position, ie. pushed in. To enable the antenna construction to transmit and receive radiofrequency radiation in the latter position, too, and to prevent the transmission signal from being reflected via the open antenna port back to the radio apparatus the construction must include a radiating element permanently connected to the antenna port of the radio apparatus. The components of the construction shall be suitable for large-scale mass production where the mechanical tolerances are determined on the basis of the desired operating frequency and bandwidth of the antenna. Lately, a lot of attention has also been paid to the fact that radio-frequency radiation from the antenna should be directed, as much as possible, away from the user of the portable radio apparatus so as not be absorbed by him.
In this patent application we will discuss a mobile or wireless telephone as an example of a portable radio apparatus. Typical known antenna constructions in these apparatuses meeting at least part of the aforementioned requirements include various combinations of helix and whip elements. The movable part of an antenna construction usually consists of a whip element, ie. a straight conductor, which can be pulled out along its longitudinal axis and pushed inside the body of the telephone. The helix element, or a cylindrical coil conductor, is connected either to the top end of the whip element, in which case it moves with the whip element, or to the body of the telephone, in which case the whip element may move through the helix element. Different ways to create an electric coupling between the antenna port of the radio apparatus and the antenna elements as well as from an antenna element to another are disclosed e.g. in the Finnish patent application no. 952742, "Kaksitoiminen antenni".
However, constructions according to the prior art prove problematic as the operating frequencies of portable radio apparatuses become higher and higher. New cellular radio systems, such as the personal communication network (PCN) and personal communication system (PCS) operate at 1.8 to 2 GHz, wherein the radiation wavelength is about 15 cm and a radiating antenna element dimensioned according to a quarter of the wavelength is only a few centimeters in length. To manufacture prior art helix elements in series production in such a manner that dimensional fluctuation will not significantly affect the electrical characteristics of the antennas sets strict requirements on the manufacturing process. Attempts to reduce radiation directed to the user have usually led to clumsy shield arrangements that have numerous parts and are relatively expensive to manufacture.